Often times a given transceiver system is required to operate under widely varying conditions. When the distance between local and remote transceivers varies greatly, the power required to communicate varies accordingly. In the far field, the power required is dictated by the inverse square law: ideally, every time the distance is doubled the power required must be quadrupled. Other factors also impinge on the ability of two transceivers to communicate. Multipath and outside RF source interference can further effect the required transmission level.
In the field of self contained, low power remote transceivers of the type used in RFID tags, there is the added design constraint of package size, available power, and cost. Typically, RFID tags must be small and light-weight, about the size of your average WHEAT THIN brand crackers. Often, this requires the transceiver circuitry be incorporated into a single integrated circuit chip with a very small battery as a power supply.
To conserve the limited power afforded by a small battery, signal transmissions should be as efficient as possible. The tag should use as little power as possible during non-communicating operation. Simpler circuit design dissipates less power and is cheaper to construct.